The present invention relates to a novel member of the tumor necrosis factor family of receptors. More specifically, isolated nucleic acid molecules are provided encoding a novel human tumor necrosis factor receptor, TR9 (also known as Death Domain Containing Receptor 6, or simply DR6). TR9 polypeptides are also provided, as are vectors, host cells and recombinant methods for producing the same. The invention further relates to screening methods for identifying agonists and antagonists of TR9 activity.
Many biological actions, for instance, response to certain stimuli and natural biological processes, are controlled by factors, such as cytokines. Many cytokines act through receptors by engaging the receptor and producing an intra-cellular response.
For example, tumor necrosis factors (TNF) alpha and beta are cytokines, which act through TNF receptors to regulate numerous biological processes, including protection against infection and induction of shock and inflammatory disease. The TNF molecules belong to the xe2x80x9cTNF-ligandxe2x80x9d superfamily, and act together with their receptors or counter-ligands, the xe2x80x9cTNF-receptorxe2x80x9d superfamily. So far, nine members of the TNF ligand superfamily have been identified and ten members of the TNF-receptor superfamily have been characterized.
Among the ligands there are included TNF-xcex1, lymphotoxin-xcex1(LT-xcex1, also known as TNF-xcex2), LT-xcex2(found in complex heterotrimer LT-xcex12-xcex2), FasL, CD40L, CD27L, CD30L, 4-IBBL, OX40L and nerve growth factor (NGF). The superfamily of TNF receptors includes the p55TNF receptor, p75TNF receptor, TNF receptor-related protein, FAS antigen or APO-1, CD40, CD27, CD30, 4-IBB, OX40, low affinity p75 and NGF-receptor (Meager, A., Biologicals 22:291-295 (1994)).
Many members of the TNF-ligand superfamily are expressed by activated T-cells, implying that they are necessary for T-cell interactions with other cell types which underlie cell ontogeny and functions. (Meager, A., supra).
Considerable insight into the essential functions of several members of the TNF receptor family has been gained from the identification and creation of mutants that abolish the expression of these proteins. For example, naturally occurring mutations in the FAS antigen and its ligand cause lymphoproliferative disease (Watanabe-Fukunaga. et al., Nature 356:314 (1992)), perhaps reflecting a failure of programmed cell death. Mutations of the CD40 ligand cause an X-linked immunodeficiency state characterized by high levels of immunoglobulin M and low levels of immunoglobulin G in plasma, indicating faulty T-cell-dependent B-cell activation (Allen et al., Science 259:990 (1993)). Targeted mutations of the low affinity nerve growth factor receptor cause a disorder characterized by faulty sensory innovation of peripheral structures (Lee et al., Cell 69:737 (1992)).
TNF and LT-xcex1 are capable of binding to two TNF receptors (the 55- and 75-kd TNF receptors). A large number of biological effects elicited by TNF and LT-xe2x88x9d, acting through their receptors, include hemorrhagic necrosis of transplanted tumors, cytotoxicity, a role in endotoxic shock, inflammation, immunoregulation, proliferation and anti-viral responses, as well as protection against the deleterious effects of ionizing radiation. TNF and LT-xcex1 are involved in the pathogenesis of a wide range of diseases, including endotoxic shock, cerebral malaria, tumors, autoimmune disease, AIDS and graft-host rejection (Beutler et al., Science 264:667-668 (1994)). Mutations in the p55 receptor cause increased susceptibility to microbial infection.
Moreover, an about 80 amino acid domain near the C-terminus of TNFR1 (p55) and Fas was reported as the xe2x80x9cdeath domain,xe2x80x9d which is responsible for transducing signals for programmed cell death (Tartaglia et al., Cell 74:845 (1993)).
Apoptosis, or programmed cell death, is a physiologic process essential to the normal development and homeostasis of multicellular organisms (Steller, Science 267:1445-1449 (1995)). Derangements of apoptosis contribute to the pathogenesis of several human diseases including cancer, neurodegenerative disorders, and acquired immune deficiency syndrome (Thompson C. B., Science 267:1456-1462 (1995)). Recently, much attention has focused on the signal transduction and biological function of two cell surface death receptors, Fas/APO-1 and TNFR-1 (Cleveland et al., Cell 81:479-482 (1995); Fraser et al., Cell 85:781-784 (1996); S. Nagata et al., Science 267:1449-56 (1995)). Both are members of the TNF receptor family, which also include TNFR-2, low affinity NGFR, CD40, and CD30, among others (Smith et al., Science 248:1019-23 (1990); Tewari et al., in Modular Texts in Molecular and Cell Biology: M. Purton, Heldin, Carl, Ed. (Chapman and Hall, London, 1995). While family members are defmed by the presence of cysteine-rich repeats in their extracellular domains, Fas/APO-1 and TNFR-1 also share a region of intracellular homology, appropriately designated the xe2x80x9cdeath domain,xe2x80x9d which is distantly related to the Drosophila suicide gene, reaper (Golstein et al., Cell 81:185-6 (1995); White et al., Science 264:677-83 (1994)). This shared death domain suggests that both receptors interact with a related set of signal transducing molecules that, until recently, remained unidentified. Activation of Fas/APO-1 recruits the death domain-containing adapter molecule FADD/MORT1 (Chinnaiyan et al., Cell 81:505-512 (1995); Boldin et al., J. Biol. Chem. 270:7795-8 (1995); Kischkel et al., EMBO 14:5579-5588 (1995)), which in turn binds and presumably activates FLICE/MACH1, a member of the ICE/CED-3 family of pro-apoptotic proteases (Muzio et al., Cell 85:817-827 (1996); Boldin et al., Cell 85:803-815 (1996)). While the central role of Fas/APO-1 is to trigger cell death, TNFR-1 can signal an array of diverse biological activities-many of which stem from its ability to activate NF-kB (Tartaglia et al., Immunol Today 13:151-153 (1992)). Accordingly, TNFR-1 recruits the multivalent adapter molecule TRDAD, which like FADD, also contains a death domain (Hsu et al., Cell 81:495-504 (1995); Hsu et al., Cell 84:299-308 (1996)). Through its associations with a number of signaling molecules including FADD, TRAF2, and RIP, TRADD can signal both apoptosis and NF-KB activation (Hsu et al., Cell 84:299-308 (1996); Hsu et al., Immunity 4:387-396 (1996)).
The effects of TNF family ligands and receptors are varied and influence numerous functions, both normal and abnormal, in the biological processes of the mammalian system. There is a clear need, therefore, for identification and characterization of additional novel TNF receptors and ligands that influence biological activity, both normally and in disease states.
The present invention provides isolated nucleic acid molecules comprising a polynucleotide encoding the TR9 receptor having the amino acid sequence shown in FIGS. 1A-D (SEQ ID NO:2) or the amino acid sequence encoded by the cDNA clone deposited as ATCC Deposit Number 209037 on May 15, 1997.
The present invention also relates to recombinant vectors, which include the isolated nucleic acid molecules of the present invention, and to host cells containing the recombinant vectors, as well as to methods of making such vectors and host cells and for using them for production of TR9 receptor polypeptides or peptides by recombinant techniques.
The invention further provides an isolated TR9 polypeptide having an amino acid sequence encoded by a polynucleotide described herein.
The present invention also provides a screening method for identifying compounds capable of enhancing or inhibiting a cellular response induced by the TR9 receptor. The method involves contacting cells which express the TR9 receptor with the candidate compound, assaying a cellular response, and comparing the cellular response to a standard cellular response, the standard being assayed when contact is made in absence of the candidate compound; whereby, an increased cellular response over the standard indicates that the compound is an agonist and a decreased cellular response over the standard indicates that the compound is an antagonist.
The invention further provides diagnostic assays such as quantitative and diagnostic assays for detecting levels of TR9 receptor protein. Thus, for instance, a diagnostic assay in accordance with the invention for detecting over-expression of TR9, or soluble form thereof, compared to normal control tissue samples, may be used to detect the presence of tumors.
Tumor Necrosis Factor (TNF) family ligands are known to be among the most pleiotropic cytokines, inducing a large number of cellular responses, including cytotoxicity, anti-viral activity, immunoregulatory activities, and the transcriptional regulation of several genes. Cellular response to TNF-family ligands include not only normal physiological responses, but also diseases associated with increased apoptosis or the inhibition of apoptosis. Apoptosis-programmed cell death-is a physiological mechanism involved in the deletion of peripheral T lymphocytes of the immune system, and its dysregulation can lead to a number of different pathogenic processes. Diseases associated with increased cell survival, or the inhibition of apoptosis, include cancers, autoimmune disorders, viral infections, inflammation, graft vs. host disease, acute graft rejection, and chronic graft rejection. Diseases associated with increased apoptosis include AIDS, neurodegenerative disorders, myelodysplastic syndromes, ischemic injury, toxin-induced liver disease, septic shock, cachexia,-and anorexia.
Thus, the invention further provides a method for enhancing apoptosis induced by a TNF-family ligand, which involves administering to a cell which expresses the TR9 polypeptide an effective amount of an agonist capable of increasing TR9 mediated signaling. Preferably, TR9 mediated signaling is increased to treat a disease wherein decreased apoptosis is exhibited.
In a further aspect, the present invention is directed to a method for inhibiting apoptosis induced by a TNF-family ligand, which involves administering to a cell which expresses the TR9 polypeptide an effective amount of an antagonist capable of decreasing TR9 mediated signaling. Preferably, TR9 mediated signaling is decreased to treat a disease wherein increased apoptosis is exhibited.